In a previously proposed technique of a Patent Document 1, a revolution frequency of an engine is reference signalized and a sound effect in accordance with the revolution frequency of the engine is outputted from an audio speaker and an acceleration time situation of a vehicle is transmitted to a driver of the vehicle by adjusting a sound pressure on a basis of a variation state of the revolution frequency of the engine.
As in the previously proposed technique described above, when the sound pressure is adjusted on a basis of only the variation state of the revolution frequency of the engine, in a vehicle which can be accelerated in a state in which a variation in an engine revolution number is small by means of, for example, a continuously variable transmission, it is difficult to accurately transmit the acceleration time situation such as an acceleration intention of the driver or an acceleration state of the vehicle.
A task of the present invention is to more accurately transmit the acceleration time situation such as the intention of the acceleration by the driver or the acceleration state of the vehicle.